1. Field of the Invention
The invention relates to a droplet jet device and, more particularly, to a construction of a jet nozzle in a droplet jet device.
2. Description of the Related Art
There is conventionally proposed an ink jet printer of a bubble jet type using an electro-heat transducer element as a pressure generating member or a piezoelectric type using an electro-mechanical transducer element as a pressure generating member. Such ink jet printers have received consumer notice because of their low noise as compared with impact type printers.
A piezoelectric type ink jet printer is called a drop on-demand system because the volume of an ink channel is changed by a change in dimension of a piezoelectric actuator. When the volume of the ink channel is decreased, ink in the ink channel is jetted from a jet nozzle, whereas when the volume of the ink channel is increased, ink is introduced through a valve into the ink channel. A plurality of such jet units are arranged close to one another and the ink is jetted from desired ones of the jet units to form characters and images on a recording medium such as a paper.
This type of droplet jet device is described, for example, in U.S. Pat. No. 4,879,568 and U.S. Pat. No. 4,887,100. FIGS. 10 and 11 schematically show a conventional droplet jet device. FIG. 10 is a sectional view of a part of an array 61 constituting the droplet jet device, a piezoelectric ceramics plate 62, polarized in a direction of arrow 51, has a plurality of side walls such as 63A, 63B, 63C, 63D and 63E. The piezoelectric ceramics plate 62 is bonded, through a bonding layer 67, to a cover plate 66 formed of a metal, glass or ceramics. With this construction, a plurality of ink channels, such as 64A, 64B, 64C and 64D are so formed as to be spaced from one another in a lateral direction as shown in FIG. 10. Each ink channel 64 is elongated along each side wall 63 and has a rectangular cross section. Each side wall 63 extends over a full length of each ink channel 64 and is deformable in the direction perpendicular to an axis of each ink channel 64 and the polarizing direction 51 to change an ink pressure supplied in the ink channel 64. A metal electrode 65, for applying a driving electric field to the side wall 63, is formed on a surface of each side wall 63. The metal electrode 65 is surface-treated to prevent corrosion by the ink.
When the jet unit 64B in the array 61 is selected according to desired print data, for example, a driving electric field is applied between the metal electrodes 65A and 65B and between the metal electrodes 65C and 65D. As the driving electric field direction and the polarizing direction are perpendicular to each other, the side wall 63B and the side wall 63C are deformed in the internal direction of the ink channel 64B by a piezoelectric thickness slip effect. This deformation causes a decrease in volume of the ink channel 64B to increase the ink pressure in the ink channel 64B. Accordingly, an ink droplet in the ink channel 64B is jetted from a jet nozzle shown in FIG. 11. When the application of the driving electric field is stopped, the side walls 63B and 63C are returned to their original positions, before deformation, so that the ink pressure in the ink channel 64B is decreased and ink is supplied from an ink supply section (not shown) into the ink channel 64B.
The above-mentioned array 61 is manufactured by the following method. As shown in FIG. 11, the piezoelectric ceramics plate 62, polarized in the direction of an arrow 51, is grooved by grinding by rotation of a diamond cutting disk to form a plurality of parallel grooves 74 constituting the above-configured ink channels 64. The above-mentioned metal electrode 65 is formed on the surface of each groove 74 by sputtering. The cover plate 66 is bonded to an upper surface 73A of the piezoelectric ceramics plate 62 on the grooves 74 side. A nozzle plate 70 having a plurality of jet nozzles 71, which correspond to the end positions of the ink channels 74, is bonded to an end surface 73B of the piezoelectric ceramics plate 62 on the ink jet side. In the step of bonding the nozzle plate, epoxy adhesive is used and it is heated at 150.degree. C. for a period of 1/2 through 1 hour to harden the epoxy adhesive. Further, when no printing is carried out, a cap 80, for preventing choking of the ink channels 74 due to drying of ink, is mounted on a front surface of the nozzle plate 70.
Accordingly, in the above mentioned conventional device, the number of parts and manufacturing steps is large, and choking of the ink channels upon bonding of the nozzle plate 70 by the epoxy adhesive often occurs. Further, a temperature of the piezoelectric transducer is increased in the step of bonding the nozzle plate, causing a deterioration in piezoelectric characteristics of the piezoelectric ceramics plate 62.